/Engine/Plugins/Runtime/XRBase/Source/XRBase/Public/HeadMountedDisplayFunctionLibrary.h
If the HMD has multiple positional tracking sensors, return a total number of them currently connected.
[UFUNCTION](Programming/UnrealArchitecture/Reference/Functions)(BlueprintPure, Category="Input|HeadMountedDisplay") static int32 GetNumOfTrackingSensors()